There is only one view of the murder of British soldier Lee Rigby on a south London street three weeks ago: horrific.

But there are two views of its significance. One is that it was an act by crazy people, motivated — in this case by a perverted notion of Islam — but is of no broader significance. Crazy people do crazy things, so don't overreact. The other view is that the ideology that inspired the murder of Rigby is profoundly dangerous.

I am of the latter view. Of course, we shouldn't overreact. We didn't after the July 7, 2005, attacks on London's public-transport system. But we did act. And we were right to do so. Our security services' actions undoubtedly prevented other serious attacks. The "Prevent" program in local communities was sensible.